As long as the breeder has some standards of hygene going on, you should be okay. If it's somebody who mixes animals, fails to wash hands between working with different sets of animals, things like that, there could be a little concern. Overall concerns should be very very small.
If it were me, I might keep it isolated more to be sure the new one is strong, healthy, and most importantly eating well, before mixing the two together...if they are compatable in size and seem to get along.